1. Field of the Invention
The present invention relates to the automated administration of liquid medicine to patients, and is particularly well suited to provide a patient controlled analgesia (PCA) system for administering analgesia as by intravenous infusion. More particularly, the present invention relates to a "dynamically" self-adjusting patient-responsive system that serves both to maintain infusion delivery of a drug within physician-prescribed limits for a particular patient, and to utilize patient input in a plurality of ways to provide "on demand" "interval dosing" to supplement a "current rate" of background delivery of the drug to the patient, so that the resulting infusion delivery of drug is conformed to a minimum that is consistent with the patient's current needs, within physician-prescribed limits.
2. Prior Art
The automated dispensing of liquid medicine, such as analgesia, as by infusion to relieve postoperative pain, to relieve pain caused by disease such as cancer, and/or to relieve other severe pain is increasingly being effected by utilizing "presettable" (i.e., "programmable") infusion pump units. Typically, an infusion pump unit is provided with a quantity of liquid analgesia, and buttons (or other suitable controls) of the pump unit are operated to "preset" or "program" the pump unit to dispense analgesia in accordance with a plan of physician-prescribed dosages. Because the drug to be dispensed often is of narcotic origin, typically morphine, care must be taken in "instructing" the pump unit as by correctly entering the prescribed series of commands that are to be carried out by the unit in order to suitably meet the needs of a particular patient.
To prevent the entry of unsuitable commands and/or the entry of commands by unauthorized persons, infusion pump units typically are provided with security features including keylock-controlled switches and requirements for entry of authorization codes (e.g., "passwords") before an infusion pump unit will recognize and carry out newly received commands.
Programmable infusion pumps have gained a reputation for performing reliably to timely dispense prescribed doses of drugs such as analgesia. In view of the reliability that has been demonstrated by infusion pump units, and inasmuch as the use of infusion pump units often helps to free trained nurses for functions other than the hour-to-hour routine administration of medication, increasingly widespread use is being made of infusion pump units in hospitals and in long term care facilities. In view of the demand that exists for these units, the units now are commercially available from a variety of medical supply houses.
In one widely marketed form, programmable infusion pumps are designed simply to provide a reliable supply of pain medication in accordance with a fixed dosage prescription provided by a physician. Pumps that are capable of providing fixed-dose modes of delivery of analgesia are described in U.S. Pat. Nos. 4,627,839 and 4,828,551 issued Dec. 9, 1986 and May 9, 1989, respectively, the disclosures of which are incorporated herein by reference.
In an updated form, and as is discussed in U.S. Pat. No. 4,627,839, some programmable infusion pumps are capable of functioning to deliver analgesia in either of two ways, namely in a fixed-dose mode of delivery, or in what is called a "patient controlled analgesia" (PCA) mode, namely a delivery mode wherein the unit is responsive to patient "input" or "demand" for analgesia, with the response of such units being constrained by physician-prescribed limits that are designed to avoid such problems as "overdose." The invention that forms the subject matter of U.S. Pat. No. 4,627,839 is intended to provide a means to "convert" existing programmable infusion pumps from a form that is capable only of operating in a fixed-dose mode of delivery to a form that will enable such pumps to operate either in a fixed-dose mode or in a PCA mode.
In still another form, Abbott Laboratories of North Chicago, Ill. 60064 has begun marketing a programmable infusion pump unit under the designation "PCA Plus, Model 4100." The Abbott unit features a capability to operate 1) in a fixed-dose delivery mode, 2) in a PCA delivery mode, or 3) in something of a combination of "fixed-dose" and "PCA" modes. In the "combined" mode, the Abbott unit can be preset to deliver analgesia simultaneously A) in a "fixed-dose" mode (wherein the resulting rate at which analgesia is delivered to the patient can be referred to as a "current rate"--i.e., a rate that is "preset" and therefore is "fixed" as opposed to being variable in response to patient demand and need), and B) in "PCA mode" response to patient demand (with the "PCA mode" providing what can be referred to as a series of "interval doses" that supplement the "current rate" delivery of analgesia).
The Abbott unit is provided with means for keeping track of the supply of analgesia that is delivered to a patient. The Abbott unit also has a number of other features including safety features that are of a type that is well known to those who are skilled in the art, with examples being 1) means for monitoring the quantity of analgesia that has been administered to the patient to prevent overdose and/or undesirable side effects that may result from doses that are excessive, and 2) means for monitoring and controlling the time interval that must transpire between consecutive administrations of "interval doses."
Not addressed by the proposal of the Abbott unit or by other prior proposals is a very important need that arises during "combined mode" delivery of analgesia to a patient (i.e., a mode that includes the dispensing of analgesia both 1) by establishing a "current rate" for delivery of a "background" dosage of analgesia, and 2) by permitting the background delivery to be supplemented by "on demand" doses that are requested by "demand" input from the patient)--namely the very real need for not only the "PCA mode" of analgesia delivery to be responsive to patient demand, but also for the "current rate mode" of analgesia delivery to likewise be responsive to patient demand.
Neither the Abbott proposal nor other prior proposals provide for a "dynamically" adjusted "resulting rate" of infusion delivery of drug to a patient--wherein the resulting infusion rate is diminished automatically in response to failure of a patient to maintain a preset "target" level of demand (e.g., a certain number of button presses per pre-set time interval). Thus, these units do not function to automatically reduce infusion rate as a patient becomes sedated, or as healing progresses, or as patient demand diminishes as the result of these or other reasons. Nor do these units function to conform the resulting infusion rate to a minimum that is consistent with current needs of a patient, within physician-prescribed limits.
In the study of analgesic medicine, it is well accepted and understood that there are no "common denominators" that will enable a physician to accurately predict the analgesia needs of particular patients, nor even to predict with accuracy how the analgesia needs of particular patients will vary depending on a host of factors that interact, such as the time of day, the level of activity of the patient, whether the patient is standing, sitting or reclining, etc. Differences in ranges of required analgesia can be dramatic even among physically similar patients who are subjected to very similar pain-producing circumstances. Thus, while systems that embody prior proposals for automated dispensing systems for analgesia are to some extent "patient controlled," the fact remains that, in a number of important ways in which these systems can be preset to effect delivery of medication, these systems are not responsive to patient need to a desired degree.
Systems that embody prior proposals do not make the fullest possible use of patient "demand" information to modify the "resulting rate" at which medication is infusion delivered to patients. Such systems are seriously and severely limited by the fact that the type of infusion delivery they provide is defined by a static set of predefined parameters--by settings that do not vary within physician-prescribed ranges based upon patient input--i.e., by settings that may be very inappropriate for a particular patient inasmuch as they were prescribed by a physician who typically is not in frequent contact with the patient, and who can only guess at the range of values that are most appropriate for use with any particular patient under the particular circumstances that are at hand.
Stated in another way, the systems of prior proposals are not nearly as "patient responsive" as they need to be in order to accommodate the very significant differences in analgesia dosage levels that are appropriate for use with different patients, or that are needed by a particular patient at different times of the day or as the patient's schedule of activities moves among states of sleep, alert restfulness, and various stages of physical exertion. Most particularly, the systems of prior proposals do not provide "dynamically" self-adjusting patient-responsive systems that serve both to maintain infusion delivery of a drug within physician-prescribed limits for a particular patient, and to utilize patient input in a plurality of ways to provide "on demand" "interval dosing" to supplement a "current rate" of background delivery of the drug to the patient, so that the resulting infusion delivery of drug is conformed to a minimum that is consistent with the patient's current needs, within physician-prescribed limits.
As regards the level of analgesia that is needed by a particular patient at a particular time, it often has been observed that the "best" pain expert for a particular patient is the patient himself or herself--as opposed to the patient's physician. While physicians may have the knowledge and experience that is needed to determine a suitable analgesia dosage range that ought to be "tried" in an effort to meet the needs of a particular patient, it tends to be the patient, not the physician, who is the best judge of the dosage within the physician-set range that best serves the needs of the patient at a particular time and under the circumstances of the moment. Thus, automated analgesia dispensing equipment that is set in accordance with input received solely from the physician has an inherent drawback.
Moreover, it has been observed that the effectiveness of the administration of analgesia often can be enhanced when the dispensing of the drug is being controlled to the fullest possible degree by the patient--with safety considerations being kept in mind to prevent overdose In some instances it has been observed that, with patient control, the quantity of a pain-relieving drug that is needed to provide a desired degree of relief is diminished, patient comfort is enhanced, and/or the severity of side effects from taking the drug is lessened. Accordingly, automated dispensing machines that make minimal use of patient input and rely primarily on physician input may, in some instances, malserve the best interests of the patient.